For an electric double layer capacitor having a coin type structure, the structure as shown in FIG. 6 is generally known. Namely, a first polarizing electrode (1) including an activated carbon or the like and a second polarizing electrode (2) including an activated carbon or the like are disposed opposite to each other with a separator (3) interposed therebetween. Thus, the first polarizing electrode (1) and the second polarizing electrode (2) are provided with a first current collector (6) and a second current collector (7), respectively. A pair of the polarizing electrodes (1) and (2), and the separator (3) are impregnated with an electrolytic solution. The components are accommodated in the storage space formed by an exterior case (5) serving as an anode terminal, and an exterior cover (4) serving as a cathode terminal. A gasket (8) having an electric insulation property is disposed between the inner circumferential part (5a) of the exterior case (5) and the outer circumferential part (4a) of the exterior cover (4). Thus, the opening tip portion (5b) of the exterior case (5) is inwardly bent. As a result, the storage space formed by the exterior case (5) and the exterior cover (4) is hermetically sealed.
The outer circumferential part (4a) of the exterior cover (4) is provided with a folded-back part (4b), which facilitates the application of pressure to the gasket (8), and allows the improvement of the airtightness (see, e.g., JP-A-8-222192).
The electric double layer capacitor as described above is mounted to a printed circuit substrate, or the like as a back-up power source for the memory of portable communication equipment, or the like, to be used. In recent years, the circuit substrate used in electronic equipment such as the portable communication equipment is required to have higher performances, to be more multifunctional, and to be more compact in size. Thus, a large number of electronic components are required to be mounted on the substrate. Under such circumstances, the following reflow soldering technique is used. A cream solder is applied to the portions on the substrate, on which electronic components such as an electric double layer capacitor are mounted. Then, the electronic components are mounted on the cream solder-applied surface, and the substrate is introduced to a reflow furnace. In the reflow furnace, the substrate is heated at a temperature as high as about 230° C. for a short time to melt the solder. As a result, the electronic components are connected to the substrate. In order to cope with such a trend for higher temperatures in the reflow soldering step, polyphenylene sulfide, or the like, excellent in elasticity, formability, and heat resistance is used as the gasket material for an electric double layer capacitor. Whereas, for the reflow soldering, lead-containing solders of a tin-lead system and the like have conventionally often been used.